strbuf: add strbuf_vaddf

In a variable-args function, the code for writing into a strbuf is
non-trivial. We ended up cutting and pasting it in several places
because there was no vprintf-style function for strbufs (which in turn
was held up by a lack of va_copy).

Now that we have a fallback va_copy, we can add strbuf_vaddf, the
strbuf equivalent of vsprintf. And we can clean up the cut and paste
mess.

Signed-off-by: Jeff King <peff@peff.net>
Improved-by: Christian Couder <christian.couder@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

fsck.c

@@ -347,26 +347,14 @@ int fsck_object(struct object *obj, int strict, fsck_error error_func)
 int fsck_error_function(struct object *obj, int type, const char *fmt, ...)
 {
 	va_list ap;
-	int len;
 	struct strbuf sb = STRBUF_INIT;
 
 	strbuf_addf(&sb, "object %s:", obj->sha1?sha1_to_hex(obj->sha1):"(null)");
 
 	va_start(ap, fmt);
-	len = vsnprintf(sb.buf + sb.len, strbuf_avail(&sb), fmt, ap);
+	strbuf_vaddf(&sb, fmt, ap);
 	va_end(ap);
 
-	if (len < 0)
-		len = 0;
-	if (len >= strbuf_avail(&sb)) {
-		strbuf_grow(&sb, len + 2);
-		va_start(ap, fmt);
-		len = vsnprintf(sb.buf + sb.len, strbuf_avail(&sb), fmt, ap);
-		va_end(ap);
-		if (len >= strbuf_avail(&sb))
-			die("this should not happen, your snprintf is broken");
-	}
-
 	error("%s", sb.buf);
 	strbuf_release(&sb);
 	return 1;

merge-recursive.c

@@ -137,7 +137,6 @@ static void flush_output(struct merge_options *o)
 __attribute__((format (printf, 3, 4)))
 static void output(struct merge_options *o, int v, const char *fmt, ...)
 {
-	int len;
 	va_list ap;
 
 	if (!show(o, v))
@@ -148,21 +147,9 @@ static void output(struct merge_options *o, int v, const char *fmt, ...)
 	strbuf_setlen(&o->obuf, o->obuf.len + o->call_depth * 2);
 
 	va_start(ap, fmt);
-	len = vsnprintf(o->obuf.buf + o->obuf.len, strbuf_avail(&o->obuf), fmt, ap);
+	strbuf_vaddf(&o->obuf, fmt, ap);
 	va_end(ap);
 
-	if (len < 0)
-		len = 0;
-	if (len >= strbuf_avail(&o->obuf)) {
-		strbuf_grow(&o->obuf, len + 2);
-		va_start(ap, fmt);
-		len = vsnprintf(o->obuf.buf + o->obuf.len, strbuf_avail(&o->obuf), fmt, ap);
-		va_end(ap);
-		if (len >= strbuf_avail(&o->obuf)) {
-			die("this should not happen, your snprintf is broken");
-		}
-	}
-	strbuf_setlen(&o->obuf, o->obuf.len + len);
 	strbuf_add(&o->obuf, "\n", 1);
 	if (!o->buffer_output)
 		flush_output(o);

strbuf.c

@@ -195,24 +195,29 @@ void strbuf_adddup(struct strbuf *sb, size_t pos, size_t len)
 
 void strbuf_addf(struct strbuf *sb, const char *fmt, ...)
 {
-	int len;
 	va_list ap;
+	va_start(ap, fmt);
+	strbuf_vaddf(sb, fmt, ap);
+	va_end(ap);
+}
+
+void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap)
+{
+	int len;
+	va_list cp;
 
 	if (!strbuf_avail(sb))
 		strbuf_grow(sb, 64);
-	va_start(ap, fmt);
+	va_copy(cp, ap);
-	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
+	len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, cp);
-	va_end(ap);
+	va_end(cp);
 	if (len < 0)
-		die("your vsnprintf is broken");
+		die("BUG: your vsnprintf is broken (returned %d)", len);
 	if (len > strbuf_avail(sb)) {
 		strbuf_grow(sb, len);
-		va_start(ap, fmt);
 		len = vsnprintf(sb->buf + sb->len, sb->alloc - sb->len, fmt, ap);
-		va_end(ap);
+		if (len > strbuf_avail(sb))
-		if (len > strbuf_avail(sb)) {
+			die("BUG: your vsnprintf is broken (insatiable)");
-			die("this should not happen, your snprintf is broken");
-		}
 	}
 	strbuf_setlen(sb, sb->len + len);
 }

strbuf.h

@@ -120,6 +120,8 @@ extern void strbuf_addbuf_percentquote(struct strbuf *dst, const struct strbuf *
 
 __attribute__((format (printf,2,3)))
 extern void strbuf_addf(struct strbuf *sb, const char *fmt, ...);
+__attribute__((format (printf,2,0)))
+extern void strbuf_vaddf(struct strbuf *sb, const char *fmt, va_list ap);
 
 extern size_t strbuf_fread(struct strbuf *, size_t, FILE *);
 /* XXX: if read fails, any partial read is undone */

trace.c

@@ -64,28 +64,18 @@ static const char err_msg[] = "Could not trace into fd given by "
 
 void trace_printf(const char *fmt, ...)
 {
-	struct strbuf buf;
+	struct strbuf buf = STRBUF_INIT;
 	va_list ap;
-	int fd, len, need_close = 0;
+	int fd, need_close = 0;
 
 	fd = get_trace_fd(&need_close);
 	if (!fd)
 		return;
 
 	set_try_to_free_routine(NULL);	/* is never reset */
-	strbuf_init(&buf, 64);
 	va_start(ap, fmt);
-	len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
+	strbuf_vaddf(&buf, fmt, ap);
 	va_end(ap);
-	if (len >= strbuf_avail(&buf)) {
-		strbuf_grow(&buf, len - strbuf_avail(&buf) + 128);
-		va_start(ap, fmt);
-		len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
-		va_end(ap);
-		if (len >= strbuf_avail(&buf))
-			die("broken vsnprintf");
-	}
-	strbuf_setlen(&buf, len);
 
 	write_or_whine_pipe(fd, buf.buf, buf.len, err_msg);
 	strbuf_release(&buf);
@@ -96,28 +86,18 @@ void trace_printf(const char *fmt, ...)
 
 void trace_argv_printf(const char **argv, const char *fmt, ...)
 {
-	struct strbuf buf;
+	struct strbuf buf = STRBUF_INIT;
 	va_list ap;
-	int fd, len, need_close = 0;
+	int fd, need_close = 0;
 
 	fd = get_trace_fd(&need_close);
 	if (!fd)
 		return;
 
 	set_try_to_free_routine(NULL);	/* is never reset */
-	strbuf_init(&buf, 64);
 	va_start(ap, fmt);
-	len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
+	strbuf_vaddf(&buf, fmt, ap);
 	va_end(ap);
-	if (len >= strbuf_avail(&buf)) {
-		strbuf_grow(&buf, len - strbuf_avail(&buf) + 128);
-		va_start(ap, fmt);
-		len = vsnprintf(buf.buf, strbuf_avail(&buf), fmt, ap);
-		va_end(ap);
-		if (len >= strbuf_avail(&buf))
-			die("broken vsnprintf");
-	}
-	strbuf_setlen(&buf, len);
 
 	sq_quote_argv(&buf, argv, 0);
 	strbuf_addch(&buf, '\n');